1. Field of the Invention
This invention relates to a laboratory material and, more particularly, to a stable blood serum bilirubin referencce composition.
2. Description of the Prior Art
A concentration of bilirubin of 20 milligram per 100 milliliter (20 mg%) is used as a criteria by physicans for determining at which point one must transfuse a newborn infant so that there is no brain damage. This procedure usually occurs with newborn infants who undergo considerable trauma during the birth process. The newborn will either be transfused or blood exchanged on the basis of a bilirubin test.
At present, controls are made by a lyophilization process to stabilize various analytes including bilirubin. These lyophilized controls must be reconstituted by the clinical laboratory before use. The reconstituted controls are only useful as a calibrator for a maximum period of about one day. The reconstituted control slowly breaks down to lower and lower values. However, the clinical laboratory is always using the calibrator's theoretically high value which, unfortunately, can lead to erroneous results.
Prior art bilirubin reference standards have been reported to deteriorate about 2% per month when stored at -23.degree. C. This deterioration prohibits long storage at this temperaure. Bilirubin reference standards stored at 31 16.degree. C. for twelve days exhibit about a 5% deterioration at the end of this period. At -70.degree. C., bilirubin standards exhibited relatively good stability, deteriorating about 1% in six months. Tietz, Fundamentals of Clinical Chemistry, W. B. Saunders Company, Philadelphia, Penn., 2nd Edition (1976), 1035-1043, and Doumas et al., Clinical Chemistry, 19 (9):984 (1973), said publications being incorporated herein in toto by reference.